Aircraft often have an on-board auxiliary power unit to provide electrical power and compressed air to various systems. When the aircraft is on the ground, the auxiliary power unit is the primary source of power to drive the environmental control systems, air driven hydraulic pumps, and the starters for the engines. During flight, auxiliary power units may provide pneumatic and electric power.
The auxiliary power unit is typically arranged in the tailcone of an aircraft. An intake duct extends between an intake opening in the exterior surface of the tailcone and the auxiliary power unit itself. The intake duct defines an airflow passage through which air for the auxiliary power unit is drawn. A ram door assembly at the intake opening selectively opens and closes depending on auxiliary power unit and/or aircraft requirements. The air flowing through the intake duct may be used to run the auxiliary power unit, cool the auxiliary power unit oil, and/or ventilate the auxiliary power unit compartment.
It has been found that conventional ram door assemblies may have certain disadvantages. For example, turbulence, vortices, or other distortions may form as air enters the intake opening. This reduction in efficiency in the intake airflow may impact the performance of the auxiliary power unit. Attempts to address these disadvantages may adversely impact the size and weight of the auxiliary power unit and/or the ram door assemblies. Other adjustments to the ram door assemblies may result in an increase in the overall aerodynamic resistance, e.g. the total coefficient of drag, of the aircraft.
Accordingly, it is desirable to provide improved ram door assemblies that increase the efficiency of intake airflow. In addition, it is desirable to provide such ram door assemblies while improving aerodynamic drag characteristics. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.